High-Efficiency Multilevel Multimode Dynamic Supply Switching Modulator for LTE Power Amplifier

A high efficiency multilevel multimode (MLMM) dynamic supply switching (DSS) modulator using a single-inductor multiple-output (SIMO) dc-dc converter is presented to improve the efficiency of power amplifiers (PAs) for a 900 MHz band. The efficiency improvements from the DSS PA were analyzed according to the number of switching levels using the probability density function of the modulation signal. Based on the analysis results, the proposed DSS modulator was configured to give four optimal switching levels in relation to efficiency improvement of the overall DSS PA, efficiency of the modulator itself, and circuit complexity. The SIMO dc-dc converter, which newly adopts a duty skip method, was designed to generate multiple dc voltages. In addition, the four voltage levels were reconfigured according to the average output power to further improve the efficiency of the PA through a wide output power range. The proposed MLMM DSS PA was fabricated using a 0.18 μm CMOS process. For 16-quadrature amplitude modulation long-term evolution (LTE) signals, the proposed MLMM DSS modulator exhibited an efficiency of no less than 80% in the supply power range of 0.1-1 W. Using LTE signal with 10 MHz and peak to average power ratio of 7.58 dB, the MLMM DSS PA showed power added efficiency (PAE) of 41.7% at an average power of 25 dBm with an adjacent channel leakage ratio (ACLR) of -30 dBc.